The present disclosure relates to downhole power generation and, more particularly, to generating electricity downhole using a mud operated pulser.
A wide variety of downhole well tools may be utilized which are electrically powered. For example, flow control devices, sensors, samplers, packers, instrumentation within well tools, telemetry devices, and well logging devices may all use electricity in performing their respective functions.
In the past, the most common methods of supplying electrical power to well tools were use of batteries and electrical lines extending to a remote location, such as the earth's surface. Unfortunately, some batteries cannot operate for an extended period of time at downhole temperatures, and those batteries that are able to operate downhole temperatures must still be replaced periodically. Moreover, electrical lines extending for long distances downhole can interfere with flow or access if they are positioned within a tubing string, and they can be damaged if they are positioned inside or outside of the tubing string.
Power can be generated downhole by using the circulating drilling fluid or “mud” to operate a downhole generator or turbine. Mud flow rates can vary widely and downhole generators and turbines may be adversely affected when the flow rate becomes excessively high. For example, at high flow rates the increased rotational rate produces high torques within the downhole generator or turbine. In addition, at high flow rates, more power can be generated than is necessary for the intended application, thereby leading to heat production.